The present invention relates to a process for producing pigment-coated phosphors which may be used in the production of a cathode-ray tube of a high contrast for a color television receiver and in which color filter particles (hereinafter referred to simply as "pigment") have been adhered onto the surface of phosphor particles.
More particularly, the invention pertains to a process for producing pigment-coated phosphors wherein onto the surface of a phosphor that radiates wavelengths of light corresponding to a specific portion of visible spectrum by electron-ray stimulation have been adhered pigment particles which function as a color filter that transmits wavelengths of light corresponding to the emission spectrum of the phosphor while absorbing wavelengths of light corresponding to the other portion of visible spectrum.
As a process for producing a pigment-coated phosphor, Mr. S. A. Lipp's process (U.S. Pat. No. 3,886,394) is known. According to the process, pigment-coated phosphors can be produced according to the following procedures:
(1) A pigment is milled in an aqueous solution of polyvinylpyrrolidone (hereinafter referred to simply as "PVP") for several days to 10 days and then diluted with distilled water.
(2) On the one hand, a phosphor is contacted with an aqueous gelatin solution and then washed with water.
(3) To the phosphor coated with gelatin in (2) is added the pigment coated with PVP in (1) so that the pigment may be adhered onto the surface of the phosphor.
The thus produced pigment-coated phosphor has been insufficient in adhesiveness between the pigment and the phosphor, and has a defect in that the pigment and the phosphor are separated from each other when a slurry of the phosphor is prepared, aged and then coated according to a usual method.